Lymphocyte subset reconstitution after unrelated cord blood or bone marrow transplantation in children

International audience; We report the post-transplant lymphocyte subset recovery of 226 children treated with Unrelated Cord Blood transplant (UCBT) (n = 112) or Unrelated Bone Marrow Transplant (UBMT) (n = 114) for malignant or non-malignant diseases. Absolute numbers of natural killer (NK), B and T cells were monitored by flow cytometry up to 5 years post-transplant. Immunological endpoints were: time to achieve a CD3(+) cell count > 0*5 and 1*5 × 10⁹/l, CD4(+) > 0*2 and 0*5 × 10⁹/l, CD8(+) > 0*25 ×10⁹/l, CD19(+) > 0*2 × 10⁹/l, NK > 0*1 × 10⁹/l. These endpoints were analysed through the use of cumulative incidence curves in the context of competing risks. CD8(+) T cell recovery was delayed after UCBT with a median time to reach CD8(+) T cells > 0*25 × 10⁹/l of 7*7 months whereas it was 2*8 months in UBMT (P < 0*001). B cell recovery was better in UCBT, with a median time to reach CD19(+) cells > 0*2 × 10⁹/l of 3*2 months in UCBT and 6*4 months in UBMT (P = 0*03). Median time for CD4(+) T cell and NK cell recovery was similar in UCBT and UBMT. CD4(+) T cells recovery was negatively correlated to age (better reconstitution in younger patients, P = 0*002). CD8(+) T cells recovery was shorter in recipients with a positive cytomegalovirus serology (P =0*001).